The present disclosure relates generally to subsea accumulators. More specifically, in certain embodiments the present disclosure relates to subsea accumulators comprising slow burning fuses and associated methods.
Considerable safety measures are required when drilling for oil and gas on-shore and off-shore. One such safety measure is the use of blowout preventers (BOPs). BOPs are basically large valves that close, isolate, and seal the wellbore to prevent the discharge of pressurized oil and gas from the well during a kick or other event. One type of BOP used extensively is a ram-type BOP. This type of BOP uses two opposing rams that close by moving together to either close around the pipe or to cut through the pipe and seal the wellbore.
The blowout preventers are typically operated using pressurized hydraulic fluid to control the position of the rams. Most BOPs are coupled to a fluid pump or another source of pressurized hydraulic fluid. In most applications, multiple BOPs are combined to form a BOP stack, and this may include the use of multiple types of BOPs. In some applications, several hundred gallons of pressurized hydraulic fluid may have to be stored in bottles at the BOP to be able to operate the BOP.
BOPs may be actuated by an accumulator. Traditional accumulators use a gas as a ‘spring’ to provide fluid storage at pressure. When these devices are taken subsea, the gas spring may need to be pre-charged to high pressures. This may result in very low efficiencies as the gas becomes less compressible at greater depths. A typical deepwater gas accumulator may provide only ½ gallon of “useable” fluid from an 11+ gallon accumulator. At extreme depths even greater challenges emerge as the gas becomes effectively incompressible and no longer acts as a good spring. This may require deepwater BOPs to carry more and more accumulators to achieve the necessary stored volume, creating very significant size and weight issues. A modern, deepwater BOP stack can require more than 100 accumulators in order to provide sufficient useable fluid volume.
It is desirable to develop an actuator for a blowout preventer that does not suffer from the same drawbacks of conventional actuators.